The invention relates to a flow regulator for maintaining a stable rate of flow of a fluid in a flow channel, comprising a flow-actuated element which is movable under the influence of a pressure drop in the fluid flow, and a throttle valve for regulating the fluid flow under the influence of said element.
A typical field of use for such a regulator is in connection with hydraulic pumps for unloading cargo tanks for oil or the like on e.g. a tanker, wherein the pumps are connected to and driven from a ring conduit transporting hydraulic liquid under a very high pressure, more specifically about 300 bars (30 000 kPa). Such applications utilize pumps of very large power, on the order of megawatts. In front of each pump a flow regulator is used for ensuring a stable liquid supply for the operation of the pumps in order to prevent them from "running riot" when they are about to empty the reservoir and start sucking air. Such a situation with overspeed of the pump will result in damage thereof in the course of a very short time.
Different types of regulators have been developed for this purpose. Such regulators operate to restrict or throttle the supply of hydraulic liquid as soon as changes occur in the operating conditions which may have a tendency to increase the liquid supply in the flow channel to the pump motor. The known types of flow regulators are, however, encumbered with problems in that they are complicated and in that they absorb a considerable amount of energy under normal operating conditions (i.e. with a little throttling of the liquid flow). This is a consequence of the fact that a considerable pressure drop has to be established across these known regulators in order to produce the forces used for stabilizing the through-put. With a conduit pressure of about 300 bars, it may for example be the question of a pressure drop of about 10 bars for each regulator. This in reality involves an energy loss of the order of 30 kW, which results in a substantial heating of the oil; something which in turn requires artificial cooling. It is obvious that this is economically unfavorable and also renders as the system structure more complicated.
Thus, it is an object of the invention to provide a flow regulator which is able to operate with a substantially reduced pressure drop in the flow channel in relation to the known regulators.
A further object is to provide such a flow regulator giving a more sensitive regulation with a short response time and a smoother response than what is achieved with the regulators according to the prior art.
The above-mentioned objects are achieved with a flow regulator of the introductorily stated type which, according to the invention, is characterized in that the flow-actuated element constitutes a control element for a servo means comprising a pilot valve for controlling the movement of a drive means coupled to a valve body in the throttle valve, and which, by means of the servo means, is arranged to be moved in a smooth manner independently of sudden changes in the fluid flow, the control element being arranged to be moved in the flow direction only when the rate of flow exceeds a preselected level.
In the flow regulator according to the invention, the flow-actuated element operates as a control element in a servo control of the throttle valve. By means of this technique there is achieved an efficient stabilization of the fluid flow with a very moderate pressure drop across the regulator. It is estimated that the pressure drop may be reduced to approximately 1 bar; i.e. to 1/10 of the pressure drop required in the regulators according to the prior art. The servo control absorbs some energy, but this is quite inconsequential compared to the energy lost in the existing solutions.
The flow regulator according to the invention distinguishes itself in that it has a small energy demand under normal operating conditions, and in that it maintains a stable flow level even if sudden changes in the operating conditions occur. By, inter alia, designing the throttle valve such that an efficient balancing of the pressure influencing the valve body in the throttle valve is obtained, the flow control functions well with a very moderate use of servo. Thus, by means of the utilized technique, a very "smooth" and precise flow regulation has been achieved, even with a fluid pressure of up to 300 bars.